DIFFERENTIATION-DEPENDENT EXPRESSION OF HUMAN BETA-GALACTOSIDE ALPHA-2,6-SIALYLTRANSFERASE MESSENGER-RNA IN COLON-CARCINOMA CACO-2 CELLS

We have previously documented a dramatic elevation in the activity of alpha 2,6-sialyltransferase towards Gal beta 1,4GlcNAc (EC 2.4.99.1) ( alpha 2,6ST) in CaCo-2 cells maintained in culture for several days af ter confluence to elicit a high degree of enterocytic differentiation phenotype. Northern analysis performed with a probe complementary to a region of human alpha 2,6ST mRNA common to all known transcripts demo nstrated that the expression of alpha 2,6ST mRNA in CaCo-2 cells incre ased with the degree of differentiation. When probes complementary to 5'-untranslated exons (Y + Z or X) previously identified in transcript s isolated from human placenta and from several human lymphoblastoid c ell lines were used no hybridization signal with mRNA of CaCo-2 cells was found, as reported for the mRNA of hepatoma cell line HepG2 (Wang XC, Vertino A, Eddy RL, Byers MG, Jani-Sait SN, Shows TB, Lau JTY (199 3) J Biol Chem 268: 4355-61). These results support the notion that th e major alpha 2,6ST transcript of CaCo-2 cells was the hepatoma isofor m or a new one, so far unreported. Consistent with the differentiation -dependent increase in alpha 2,6ST-mRNA expression, an elevation of th e reactivity with Sambucus nigra agglutinin of differentiated CaCo-2 c ell-surface was observed, indicating an enhanced alpha 2,6-sialylation of membrane glycoconjugates.